Cambridge, Massachusetts is home to Homer and Mary Kelly, Harvard University, the Mount Auburn Cemetary, and . . . Leonard Sheldrake. Leonard, Homer's friend, often compares the many-faceted city of Cambridge to a favorite engraving, filled with strange power and wonder, by the twentieth-century Dutch artist Maurits Escher. Leonard is a huge fan of the artist and is thrilled when Cambridge hosts an Escher exhibit. On the way to the gallery, he meets a woman in a green coat -- Frieda -- who is equally enthralled by Escher's brilliance. Leonard falls instantly in love, but Frieda hurries away without giving him any information. He is desperate to find her. Homer and Mary offer to help, but looking for her makes them feel as if they were lost in an Escher labyrinth as they encounter murders of the past, secrets of today, modern fortune-tellers, and the ghosts of Mount Auburn Cemetery.